1. Field of the Invention
The present invention relates to the process of constructing a building using shear walls, poured-in-place concrete tunnel forms, and other similar construction methods. More specifically, the present invention relates to beneficially distributing the seismic actions in a building constructed with stacks of shear walls or tunnel forms by coupling the shear walls at the top of the building.
2. Background and Related Art
In the construction of large residential complexes, high-rise buildings, and other multistory buildings, it is important to consider the axial, shear, and flexural forces exerted on the buildings. Axial forces are those acting parallel to the longitudinal axes of the buildings, and are typically caused by the weight of the building materials and the weight of the contents of the building. Shear forces and flexural moments act substantially perpendicular to the longitudinal axes of the buildings, and may be caused by winds or seismic activity. Because buildings act like vertical cantilever beams, the shear forces exerted on the buildings create potentially harmful bending moments and flexural demands. Thus, structural walls, beams, and other reinforcing members must be able to withstand not only axial loads but also lateral loads and the shear forces and flexural demands they create.
Shear walls are well known in the art for withstanding significant lateral loads. Shear walls may be made from a variety of building materials known by those skilled in the art. Generally, shear wall materials include fibers which resist relative movement, i.e., fibers which resist movement relative to surrounding fibers. Often, shear walls used in multistory buildings are made from poured concrete with reinforcing steel, also known as rebar.
Multistory buildings act as cantilever beams such that when lateral loads are applied to the building, the flexural resistance is greatest at the base of the building and decreases generally linearly toward the top of the building. Thus, it is often necessary to increase the thickness of the shear walls at the base of a multistory building, as well as increase the amount of reinforcing, to compensate for the increased forces and moments at the base. However, it is very desirable to maintain thin shear walls and limit the amount of reinforcing in shear walls. Thin shear walls and reduced reinforcing decreases costs and increases the speed of construction. Thinner walls with less reinforcing also increases the ductility of the walls, which leads to a reduced likelihood of distress in the building.
The advent of poured-in-place concrete tunnel construction methods has increased the cost-effectiveness and strength of multistory concrete buildings. The process of constructing a building using poured-in-place concrete tunnel construction methods is also typically called “tunnel forming” or “tunnel framing.” Construction of buildings using tunnel forming has been utilized for many years in the construction of multistory concrete buildings. Tunnel forming allows the walls and floor of a certain level of the building to be poured simultaneously. This method greatly reduces the costs associated with multistory concrete construction. There are many structures used in the tunnel forming process, such as those that are described in U.S. Pat. Nos. 4,439,064, 4,261,542, and 3,979,919, each of which is incorporated herein by reference.
However, even with tunnel forming, bottom-heavy flexural forces pose a problem. With typical shear wall structures, lateral loads from any direction cause undesired shear forces and flexural demands. With tunnel forming, shear forces acting parallel with the direction of the longitudinal axes of the horizontal concrete tunnels are slightly less problematic than shear forces acting perpendicular to these axes. Thus, even though tunnel forming partially reduces the problem with shear forces and flexural demands, it does not completely eliminate the problem. Consequently, conventional shear wall structures, tunnel form structures, as well as other building structures are susceptible to shear forces in any direction, thereby necessitating increased flexural resistance in such buildings without the use of thicker structural or shear walls, or increased reinforcing.
The present invention overcomes the deficiencies of the prior art.